Both Microsoft and Sony are offering gamers a way to upgrade select titles they have purchased for the Xbox 360 and PS3 to the Xbox One and PS4 versions. That way, you purchase the current gen game on release, and then can upgrade to the next-gen version at a heavily discounted price when it becomes available.

Sony has now revealed exactly how that digital upgrade will work for the four games it supports as part of the program, and depending on how you buy, it may require PS3 discs be inserted into a PS4 for the games to function.

Sony’s digital upgrade program supports the following titles:

Assassin’s Creed IV Black Flag

Call of Duty: Ghosts

Watch Dogs

Battlefield 4

If you purchase digital copies of those games through PSN then the upgrade to the PS4 version is simple as everything is tied to your PSN account. Things get a little more complicated if you purchase the PS3 versions on disc, though.

Each physical copy will have a code included with the disc which you need to enter on the PlayStation Store. That code is then tied to your PSN account. Then, when you get a PS4 you can purchase one of the four games mentioned above through the PlayStation Store and the discount will be automatically applied to the price you pay.

Sony wants to ensure you don’t then sell on your copy of the PS3 game, so in order to play the PS4 version you must have the PS3 game inserted into the console. So Sony has implemented some kind of verification check on the PS3 discs to make sure the upgrade was legit and you own the PS3 game.

I can understand why Sony decided to do that as it stops a glut of used PS3 games appearing on the market. But they didn’t need to do this. The code included with the PS3 versions only work once, so it’s not like you can share the disc with your friends and get the same cheap PS4 game upgrades.